1. Field of the Invention
This invention relates to vacuum capacitors generally, and more specifically, the present invention relates to a "fixed" vacuum capacitor with an electrically parallel trimmer capacitor internally connected thereto.
2. Description of the Prior Art
Hermetically sealed capacitors, such as vacuum and gas-filled capacitors, have, in the prior art, generally been of the fully variable type such as typically described in U.S. Pat. No. 3,257,590, among others, or of the fully fixed type, such as typically described in U.S. Pat. No. 3,156,852.
There are many applications for radio frequency capacitors in high-powered circuits where the range of variation (tuning or trimming) is relatively small. The use of the fully variable type vacuum capacitor in such applications is relatively uneconomical, both from cost and space utilization points of view. The fully variable vacuum capacitor as known in the prior art must necessarily allow for the relatively large axial translation of the movable plates and must include a relatively large bellows. The latter requirements results from the well-known phenomenon of bellows heating in such devices.
The use of the fixed type vacuum capacitor, while resulting in very good performance and space economy, frequently leaves the designer with the additional problem of circuit trimming or fine tuning. Such fine tuning or trimming is very often necessary in a radio frequency circuit because of the tolerances, not only of the capacitor itself, but of the associated circuit elements. Those skilled in this art will recognize other situations which inherently require relatively small percentage adjustment in the value of capacitance used.
In using the fully fixed capacitor, the need for additional external adjustment is presented, and cost and space advantages obtained through the use of a fixed vacuum capacitor may well be more than offset.
The manner in which the present invention deals with the prior art disadvantages will be evident as this description proceeds.